Thousands of Brentford supporters are expected to buy blackmarket tickets after an administrative blunder saw them miss out on the club's 3,200 allocation.

Allen fears that their presence in the home fans' sections of St Mary's could be a catalyst for crowd trouble.

The Brentford manager said this morning: "This is potential trouble. We are talking about people's lives, women and children going to watch the FA Cup.

"It's up to the powers that be to sort out some segregation and get these people moved. If there's trouble or a disaster at the game, afterwards some people will have to look at themselves in the mirror and ask why it has happened.

"Surely the police must look at this and review it? Our football club has said they have not got enough tickets.

"There will be 6,000 Brentford supporters at the game and - whatever the rights and wrongs of that - we are talking about supporters' safety. I find it quite ridiculous, a potential nightmare.

"We have 3,200 people with legitimate tickets, but there will be numerous tickets available for Brentford supporters, we all know it happens.

"Some have bought tickets this way already and it will continue because it's such a big game for this club. You cannot blame them.

"I know the rules say you shouldn't mix fans, but it's going to happen and some people have got to get their heads out of the sand. The ground will be invaded."

Southampton originally offered Brentford 4,750 tickets on a " guaranteed sale" basis, which would have forced the hard-up club to pay for any left unsold.

The alternative was a smaller allocation of 3,200 on a "sale or return" basis.

Brentford underestimated demand, taking this second option, then compounded the problem by giving no priority to season-ticket holders or supporters' trust members when the tickets went on sale last Monday.

The allocation sold out in three hours, leaving hundreds aggrieved.

With the game unlikely to sell out, Brentford asked for more tickets, but Southampton refused.

A Hampshire police spokesman said: "We are aware of ticketing problems for the match. We have a full police operation in place and will deal with any problems if they arise. We have no control over ticket allocation."

No tickets will be available on the day for Brentford fans, the police warned.

Chairman Rupert Lowe said: "The lesson from this is forward planning. Hopefully the Brentford fans that do come will enjoy the day - but not too much. It is regrettable that more cannot come."

Allen also revealed that Brentford are conducting an internal review into their part in the ticket fiasco and that he will be making his own personal tickets for the match available to supporters.